Iron nitride permanent magnet and technique for forming iron nitride permanent magnet

ABSTRACT

A permanent magnet may include a Fe16N2 phase constitution. In some examples, the permanent magnet may be formed by a technique that includes straining an iron wire or sheet comprising at least one iron crystal in a direction substantially parallel to a &lt;001&gt; crystal axis of the iron crystal; nitridizing the iron wire or sheet to form a nitridized iron wire or sheet; annealing the nitridized iron wire or sheet to form a Fe16N2 phase constitution in at least a portion of the nitridized iron wire or sheet; and pressing the nitridized iron wires and sheets to form bulk permanent magnet.

This application is a national stage entry under 35 U.S.C. § 371 ofInternational Application No. PCT/US2012/051382, filed Aug. 17, 2012,which claims the benefit of application No. 61/524,423, filed Aug. 17,2011. The entire contents of International Application No.PCT/US2012/051382 and U.S. Provisional Patent Application 61/524,423 areincorporated herein by reference.

The invention was made with government support under award DE-AR0000199awarded by the Department of Energy. The government has certain rightsto the invention.

GOVERNMENT RIGHTS

This invention was made with government support under ARPA-E 0472-1595awarded by the Dept. of Energy. The government has certain rights in theinvention.

TECHNICAL FIELD

The disclosure relates to permanent magnets and techniques for formingpermanent magnets.

BACKGROUND

Permanent magnets play a role in many electro-mechanical systems,including, for example, alternative energy systems. For example,permanent magnets are used in electric motors or generators, which maybe used in vehicles, wind turbines, and other alternative energymechanisms. Many permanent magnets in current use include rare earthelements, such as neodymium. These rare earth elements are in relativelyshort supply, and may face increased prices and/or supply shortages inthe future. Additionally, some permanent magnets that include rare earthelements are expensive to produce. For example, fabrication of NdFeBmagnets generally includes crushing material, compressing the material,and sintering at temperatures over 1000° C.

SUMMARY

In general, this disclosure is directed to bulk permanent magnets thatinclude Fe₁₆N₂ and techniques for forming bulk permanent magnets thatinclude Fe₁₆N₂. Bulk Fe₁₆N₂ permanent magnets may provide an alternativeto permanent magnets that include a rare earth element. Iron andnitrogen are abundant elements, and thus are relatively inexpensive andeasy to procure. Additionally, experimental evidence gathered from thinfilm Fe₁₆N₂ permanent magnets suggests that bulk Fe₁₆N₂ permanentmagnets may have desirable magnetic properties, including an energyproduct of as high as about 134 MegaGauss*Oerstads (MGOe), which isabout two times the energy product of NdFeB (about 60 MGOe). The highenergy product of Fe₁₆N₂ magnets may provide high efficiency forapplications in electric motors, electric generators, and magneticresonance imaging (MRI) magnets, among other applications.

In some aspects, the disclosure describes techniques for forming bulkFe₁₆N₂ permanent magnets. The techniques may generally include strainingan iron wire or sheet, that includes at least one body centered cubic(bcc) iron crystal, along a direction substantially parallel to a <001>crystal axis of the at least one bcc iron crystal. In some examples, the<001> crystal axis of the at least one iron wire or sheet may liesubstantially parallel to a major axis of the iron wire or sheet. Thetechniques then include exposing the iron wire or sheet to a nitrogenenvironment to introduce nitrogen into the iron wire or sheet. Thetechniques further include annealing the nitridized iron wire or sheetto order the arrangement of iron and nitrogen atoms and form the Fe₁₆N₂phase constitution in at least a portion of the iron wire or sheet. Insome examples, multiple Fe₁₆N₂ wires or sheets can be assembled withsubstantially parallel <001> axes and the multiple Fe₁₆N₂ wires orsheets can be pressed together to form a permanent magnet including aFe₁₆N₂ phase constitution.

In some aspects, the disclosure describes techniques for forming singlecrystal iron nitride wires and sheets. In some examples, a Crucibletechnique, such as that described herein, may be used to form singlecrystal iron nitride wires and sheets. In addition to such Crucibletechniques, such single crystal iron wires and sheets may be formed byeither the micro melt zone floating or pulling from a micro shaper.Furthermore, techniques for forming crystalline textured (e.g., withdesired crystalline orientation along the certain direction of wires andsheets) iron nitride wires and sheet are also described.

In one example, the disclosure is directed to a method that includesstraining an iron wire or sheet comprising at least one iron crystal ina direction substantially parallel to a <001> crystal axis of the ironcrystal; nitridizing the iron wire or sheet to form a nitridized ironwire or sheet; and annealing the nitridized iron wire or sheet to form aFe₁₆N₂ phase constitution in at least a portion of the nitridized ironwire or sheet.

In another example, the disclosure is directed to a system that includesmeans for straining an iron wire or sheet comprising at least one bodycentered cubic (bcc) iron crystal in a direction substantially parallelto a <001> axis of the bcc iron crystal; means for heating the strainediron wire or sheet; means for exposing the strained iron wire or sheetto an atomic nitrogen precursor to form a nitridized iron wire or sheet;and means for annealing the nitridized iron wire or sheet to form aFe₁₆N₂ phase constitution in at least a portion of the nitridized ironwire or sheet.

In another aspect, the disclosure is directed to a method that includesurea as an effective atomic nitrogen source to diffuse nitrogen atomsinto iron to form a nitridized iron wire or sheet or bulk.

In another aspect, the disclosure is directed to a permanent magnet thatincludes a wire comprising a Fe₁₆N₂ phase constitution.

In another aspect, the disclosure is directed to a permanent magnet thatincludes a sheet comprising a Fe₁₆N₂ phase constitution.

In another aspect, the disclosure is directed to a permanent magnet thatincludes a Fe₁₆N₂ phase constitution. According to this aspect of thedisclosure, the permanent magnet has a size in at least one dimension ofat least 0.1 mm

The details of one or more examples of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the disclosure will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow diagram that illustrates an example technique forforming a bulk Fe₁₆N₂ permanent magnet.

FIG. 2 is a conceptual diagram illustrating an example apparatus withwhich an iron wire or sheet can be strained and exposed to nitrogen.

FIG. 3 illustrates further detail of one example of the Crucible heatingstage shown in FIG. 2.

FIG. 4 is a conceptual diagram that shows eight (8) iron unit cells in astrained state with nitrogen atoms implanted in interstitial spacesbetween iron atoms.

FIGS. 5A and 5B are conceptual diagrams that illustrate an example ofthe compression process for combining multiple iron wires or sheets intoa permanent magnet.

FIG. 6 is a conceptual diagram illustrating another example apparatuswith which an iron wire or sheet can be strained.

FIG. 7 is a schematic diagram illustrating an example apparatus that maybe used for nitriding an iron wire or sheet via a urea diffusionprocess.

FIG. 8 is an iron nitride phase diagram.

FIGS. 9-12 are graphs of various results for example experiments carriedout to illustrate aspects of the disclosure.

FIG. 13 is a conceptual diagram illustrating an example apparatus forfast belt casting to texture an example iron nitride wire or sheet.

DETAILED DESCRIPTION

In general, the disclosure is directed to permanent magnets that includea Fe₁₆N₂ phase constitution and techniques for forming permanent magnetsthat include a Fe₁₆N₂ phase constitution. In particular, the techniquesdescribed herein are used to form bulk phase Fe₁₆N₂ permanent magnets.

Fe₁₆N₂ permanent magnets may provide a relatively high energy product,for example, as high as about 134 MGOe when the Fe₁₆N₂ permanent magnetis anisotropic. In examples in which the Fe₁₆N₂ magnet is isotropic, theenergy product may be as high as about 33.5 MGOe. The energy product ofa permanent magnetic is proportional to the product of remanentcoercivity and remanent magnetization. For comparison, the energyproduct of Nd₂Fe₁₄B permanent magnet may be as high as about 60 MGOe. Ahigher energy product can lead to increased efficiency of the permanentmagnet when used in motors, generators, or the like.

FIG. 1 is a flow diagram that illustrates an example technique forforming a bulk Fe₁₆N₂ permanent magnet. The technique of FIG. 1 will bedescribed with concurrent reference to FIGS. 2-5. FIG. 2 illustrates aconceptual diagram of an apparatus with which the iron wire or sheet canbe strained and exposed to nitrogen. FIG. 3 illustrates further detailof one example of the Crucible heating stage shown in FIG. 2.

The example apparatus of FIG. 2 includes a first roller 22, a secondroller 24, and a Crucible heating stage 26. First roller 22 and secondroller 24 are configured to receive a first end 38 and a second end 40,respectively, of an iron wire or sheet 28. Iron wire or sheet 28 definesa major axis between first end 38 and second end 40. As best seen inFIG. 3, iron wire or sheet 28 passes through an aperture 30 defined byCrucible heating stage 26. Crucible heating stage 26 includes aninductor 32 that surrounds at least a portion of the aperture 30 definedby Crucible heating stage 26.

The example technique of FIG. 1 includes straining iron wire or sheet 28along a direction substantially parallel (e.g., parallel or nearlyparallel) to a <001> axis of at least one iron crystal in the iron wireor sheet 28 (12). In some examples, iron wire or sheet 28 is formed ofiron having a body centered cubic (bcc) crystal structure.

In some examples, iron wire or sheet 28 is formed of a single bcccrystal structure. In other examples, iron wire or sheet 28 may beformed of a plurality of bcc iron crystals. In some of these examples,the plurality of iron crystals are oriented such that at least some,e.g., a majority or substantially all, of the <001> axes of individualunit cells and/or crystals are substantially parallel to the directionin which strain is applied to iron wire or sheet 28. For example, whenthe iron is formed as iron wire or sheet 28, at least some of the <001>axes may be substantially parallel to the major axis of the iron wire orsheet 28, as shown in FIGS. 2 and 3. As noted above, in some examples,single crystal iron nitride wires and sheets may be formed usingCrucible techniques. In addition to such Crucible techniques, singlecrystal iron wires and sheets may be formed by either the micro meltzone floating or pulling from a micro shaper to form iron wire or sheet28.

In some examples, iron wire or sheet 28 may have a crystalline texturedstructure. Techniques may be used to form crystalline textured (e.g.,with desired crystalline orientation along the certain direction ofwires and sheets) iron wires or sheet 28. FIG. 13 is a conceptualdiagram illustrating one example apparatus 70 for fast belt casting totexture an example iron wire or sheet, such as iron wire or sheet 28. Asshown fast belt casting apparatus 70 includes ingot chamber 76 whichcontains molten iron ingot 72, which may be heated by heating source 74,e.g., in the form of a heating coil. Ingot 72 flow out of chamber 76through nozzle head 78 to form iron strip 80. Iron strip 80 is fed intothe gap zone between surface of pinch rollers 82A and 82B, which arerotated in opposite directions. In some examples, the rotation of roller82A and 82B may vary from approximately 10 to 1000 rotations per minute.Iron strip cools on pinch rollers 82A and 82B and, after being pressedbetween pinch rollers 82A and 82B, forms textured iron strips 84A and84B. In some examples, texted iron strips 84A and 84B may form texturediron ribbon with thickness between, e.g., about one micrometer and abouta millimeter (either individually or after compression of multiple ironstrips.

In an unstrained iron bcc crystal lattice, the <100>, <010>, and <001>axes of the crystal unit cell may have substantially equal lengths.However, when a force, e.g., a tensile force, is applied to the crystalunit cell in a direction substantially parallel to one of the crystalaxes, e.g., the <001> crystal axis, the unit cell may distort and theiron crystal structure may be referred to as body centered tetragonal(bct). For example, FIG. 4 is a conceptual diagram that shows eight (8)iron unit cells in a strained state with nitrogen atoms implanted ininterstitial spaces between iron atoms. The example in FIG. 4 includesfour iron unit cells in a first layer 42 and four iron unit cells in asecond layer 44. Second layer 44 overlays first layer 42 and the unitcells in second layer 44 are substantially aligned with the unit cellsin first layer 42 (e.g., the <001> crystal axes of the unit cells aresubstantially aligned between the layers). As shown in FIG. 4, the ironunit cells are distorted such that the length of the unit cell along the<001> axis is approximately 3.14 angstroms (Å) while the length of theunit cell along the <010> and <100> axes is approximately 2.86 Å. Theiron unit cell may be referred to as a bct unit cell when in thestrained state. When the iron unit cell is in the strained state, the<001> axis may be referred to as the c-axis of the unit cell.

The stain may be exerted on iron wire or sheet 28 using a variety ofstrain inducing apparatuses. For example, as shown in FIG. 2, first end38 and second end 40 of iron wire or sheet 28 may received by (e.g.,wound around) first roller 22 and second roller 24, respectively, androllers 22, 24 may be rotated in opposite directions (indicated byarrows 34 and 35 in FIG. 2) to exert a tensile force on the iron wire orsheet 28.

In other examples, opposite ends of iron wire or sheet 28 may be grippedin mechanical grips, e.g., clamps, and the mechanical grips may be movedaway from each other to exert a tensile force on the iron wire or sheet28. FIG. 6 is a conceptual diagram illustrating another exampleapparatus with which iron wire or sheet 28 can be strained as describedherein. As shown, apparatus 54 includes clamps 56 and 58 which maysecure opposing ends of iron wire or sheet 28 by tightening screws 60a-d. Once iron wire or sheet is secured in apparatus 19, bolt 62 may beturned to rotate the threaded body of bolt 62 to increase the distancebetween clamps 56 and 58 and exert a tensile force on iron wire or sheet28. The value of the elongation or stress generated by the rotation ofbolt 62 may be measured by any suitable gauge, such as, e.g., a straingauge. In some examples, apparatus 54 may be placed in a furnace (e.g.,a tube furnace) or other heated environment so that iron wire or sheet28 may be heated during and/or after iron wire or sheet 28 is stretchedby apparatus 54.

A strain inducing apparatus may strain iron wire or sheet 28 to acertain elongation. For example, the strain on iron wire or sheet 28 maybe between about 0.3% and about 7%. In other examples, the strain oniron wire or sheet 28 may be less than about 0.3% or greater than about7%. In some examples, exerting a certain strain on iron wire or sheet 28may result in a substantially similar strain on individual unit cells ofthe iron, such that the unit cell is elongated along the <001> axisbetween about 0.3% and about 7%.

Iron wire or sheet 28 may have any suitable diameter and/or thickness.In some examples, a suitable diameter and/or thickness may be on theorder of micrometers (μm) or millimeters (mm) For example, an iron wiremay have a diameter greater than about 10 μm (0.01 mm). In someexamples, the iron wire has a diameter between about 0.01 mm and about 1mm, such as about 0.1 mm. Similarly, an iron sheet may have any suitablethickness and/or width. In some examples, the iron sheet may have athickness greater than about 0.01 mm, such as between about 0.01 mm andabout 1 mm, or about 0.1 mm. In some implementations, a width of theiron sheet may be greater than a thickness of the iron sheet.

A diameter of the iron wire or cross-sectional area of the iron sheet(in a plane substantially orthogonal to the direction in which the ironsheet is stretched/strained) may affect an amount of force that must beapplied to iron wire or sheet 28 to result in a given strain. Forexample, the application of approximately 144 N of force to an iron wirewith a diameter of about 0.1 mm may result in about a 7% strain. Asanother example, the application of approximately 576 N of force to aniron wire with a diameter of about 0.2 mm may result in about a 7%strain. As another example, the application of approximately 1296 N offorce to an iron wire with a diameter of about 0.3 mm may result inabout a 7% strain. As another example, the application of approximately2304 N of force to an iron wire with a diameter of about 0.4 mm mayresult in about a 7% strain. As another example, the application ofapproximately 3600 N of force to an iron wire with a diameter of about0.5 mm may result in about a 7% strain.

In some examples, iron wire or sheet 28 may include dopant elementswhich serve to stabilize the Fe₁₆N₂ phase constitution once theF_(e16)N₂ phase constitution has been formed. For example, the phasestabilization dopant elements may include cobalt (Co), titanium (Ti),copper (Cu), zinc (Zn), or the like.

As the strain inducing apparatus exerts the strain on iron wire or sheet28 and/or once the strain inducing apparatus is exerting a substantiallyconstant strain on the iron wire or sheet 28, iron wire or sheet 28 maybe nitridized (14). In some examples, during the nitridization process,iron wire or sheet 28 may be heated using a heating apparatus. Oneexample of a heating apparatus that can be used to heat iron wire orsheet 28 is Crucible heating stage 26, shown in FIGS. 2 and 3.

Crucible heating stage 26 defines aperture 30 through which iron wire orsheet 28 passes (e.g., in which a portion of iron wire or sheet 28 isdisposed). In some examples, no portion of Crucible heating stage 26contacts iron wire or sheet 28 during the heating of iron wire or sheet28. In some implementations, this is advantageous as it lower a risk ofunwanted elements or chemical species contacting and diffusing into ironwire or sheet 28. Unwanted elements or chemical species may affectproperties of iron wire or sheet 28; thus, it may be desirable to reduceor limit contact between iron wire or sheet 28 and other materials.

Crucible heating stage 26 also includes an inductor 32 that surrounds atleast a portion of aperture 30 defined by Crucible heating stage 26.Inductor 32 includes an electrically conductive material, such asaluminum, silver, or copper, through which an electric current may bepassed. The electric current may by an alternating current (AC), whichmay induce eddy currents in iron wire or sheet 28 and heat the iron wireor sheet 28. In other examples, instead of using Crucible heating stage26 to heat iron wire or sheet 28, other non-contact heating sources maybe used. For example, a radiation heat source, such as an infrared heatlamp, may be used to heat iron wire or sheet 28. As another example, aplasma arc lamp may be used to heat iron wire or sheet 28.

Regardless of the heating apparatus used to heat iron wire or sheet 28during the nitridizing process, the heating apparatus may heat iron wireor sheet 28 to temperature for a time sufficient to allow diffusion ofnitrogen to a predetermined concentration substantially throughout thethickness or diameter of iron wire or sheet 28. In this manner, theheating time and temperature are related, and may also be affected bythe composition and/or geometry of iron wire or sheet 28. For example,iron wire or sheet 28 may be heated to a temperature between about 125°C. and about 600° C. for between about 2 hours and about 9 hours. Insome examples, iron wire or sheet 28 may be heated to a temperaturebetween about 500° C. and about 600° C. for between about 2 hours andabout 4 hours.

In some examples, iron wire or sheet 28 includes an iron wire with adiameter of about 0.1 mm. In some of these examples, iron wire or sheet28 may be heated to a temperature of about 125° C. for about 8.85 hoursor a temperature of about 600° C. for about 2.4 hours. In general, at agiven temperature, the nitridizing process time may be inverselyproportional to a characteristic dimension squared of iron wire or sheet28, such as a diameter of an iron wire or a thickness of an iron sheet.

In addition to heating iron wire or sheet 28, nitridizing iron wire orsheet 28 (14) includes exposing iron wire or sheet 28 to an atomicnitrogen substance, which diffuses into iron wire or sheet 28. In someexamples, the atomic nitrogen substance may be supplied as diatomicnitrogen (N₂), which is then separated (cracked) into individualnitrogen atoms. In other examples, the atomic nitrogen may be providedfrom another atomic nitrogen precursor, such as ammonia (NH₃). In otherexamples, the atomic nitrogen may be provided from urea (CO(NH₂)₂).

The nitrogen may be supplied in a gas phase alone (e.g., substantiallypure ammonia or diatomic nitrogen gas) or as a mixture with a carriergas. In some examples, the carrier gas is argon (Ar). The gas or gasmixture may be provided at any suitable pressure, such as between about0.001 Torr (about 0.133 pascals (Pa)) and about 10 Torr (about 1333 Pa),such as between about 0.01 Torr (about 1.33 Pa) and about 0.1 Torr(about 13.33 Torr). In some examples, when the nitrogen is delivered aspart of a mixture with a carrier gas, the partial pressure of nitrogenor the nitrogen precursor (e.g., NH₃) may be between about 0.02 andabout 0.1.

The nitrogen precursor (e.g., N₂ or NH₃) may be cracked to form atomicnitrogen substances using a variety of techniques. For example, thenitrogen precursor may be heated using radiation to crack the nitrogenprecursor to form atomic nitrogen substances and/or promote reactionbetween the nitrogen precursor and iron wire or sheet 28. As anotherexample, a plasma arc lamp may be used to split the nitrogen precursorto form atomic nitrogen substances and/or promote reaction between thenitrogen precursor and iron wire or sheet 28.

In some examples, iron wire or sheet 28 may be nitridized (14) via aurea diffusion process, in which urea is utilized as a nitrogen source(e.g., rather than diatomic nitrogen or ammonia). Urea (also referred toas carbamide) is an organic compound with the chemical formula CO(NH₂)₂that may be used in some cases as a nitrogen release fertilizer. Tonitridize iron wire or sheet 28 (14), urea may heated, e.g., within afurnace with iron wire or sheet 28, to generate decomposed nitrogenatoms which may diffuse into iron wire or sheet 28. As will be describedfurther below, the constitution of the resulting nitridized ironmaterial may controlled to some extent by the temperature of thediffusion process as well as the ratio (e.g., the weight ratio) of ironto urea used for the process. In other examples, iron wire or sheet 28may be nitridized by an implantation process similar to that used insemiconductor processes for introducing doping agents.

FIG. 7 is a schematic diagram illustrating an example apparatus 64 thatmay be used for nitriding iron wire or sheet 28 via a urea diffusionprocess. Such a urea diffusion process may be used to nitriding ironwire or sheet 28, e.g., when having a single crystal iron, a pluralityof crystal structure, or textured structure. Moreover, iron materialswith different shapes, such as wire, sheet or bulk, can also be diffusedusing such a process. For wire material, the wire diameter may bevaried, e.g., from several micrometers to millimeters. For sheetmaterial, the sheet thickness may be from, e.g., several nanometers tomillimeters. For bulk material, the material weight may be from, e.g.,about 1 milligram to kilograms.

As shown, apparatus 64 includes crucible 66 within vacuum furnace 68.Iron wire or sheet 28 is located within crucible 66 along with thenitrogen source of urea 72. As shown in FIG. 7, a carrier gas includingAr and hydrogen is fed into crucible 66 during the urea diffusionprocess. In other examples, a different carrier gas or even no carriergas may be used. In some examples, the gas flow rate within vacuumfurnace 68 during the urea diffusion process may be betweenapproximately 5 standard cubic centimeters per minute (sccm) toapproximately 50 sccm, such as, e.g., 20 standard cubic centimeters perminute (sccm) to approximately 50 sccm or 5 standard cubic centimetersper minute (sccm) to approximately 20 sccm.

Heating coils 70 may heat iron wire or sheet 28 and urea 72 during theurea diffusion process using any suitable technique, such as, e.g., eddycurrent, inductive current, radio frequency, and the like. Crucible 66may be configured to withstand the temperature used during the ureadiffusion process. In some examples, crucible 66 may be able towithstand temperatures up to approximately 1600° C.

Urea 72 may be heated with iron wire or sheet 28 to generate nitrogenthat may diffuse into iron wire or sheet 28 to form an iron nitridematerial. In some examples, urea 72 and iron wire or sheet 28 may heatedto approximately 650° C. or greater within crucible 66 followed bycooling to quench the iron and nitrogen mixture to form an iron nitridematerial having a Fe₁₆N₂ phase constitution substantially throughout thethickness or diameter of iron wire or sheet 28. In some examples, urea72 and iron wire or sheet 28 may heated to approximately 650° C. orgreater within crucible 66 for between approximately 5 minutes toapproximately 1 hour. In some examples, urea 72 and iron wire or sheet28 may be heated to between approximately 1000° C. to approximately1500° C. for several minutes to approximately an hour. The time ofheating may depend on nitrogen thermal coefficient in differenttemperature. For example, if the iron wire or sheet is thickness isabout 1 micrometer, the diffusion process may be finished in about 5minutes at about 1200° C., about 12 minutes at 1100° C., and so forth.

To cool the heated material during the quenching process, cold water maybe circulated outside the crucible to rapidly cool the contents. In someexamples, the temperature may be decreased from 650° C. to roomtemperature in about 20 seconds.

As will be described below, in some examples, the temperature of urea 72and iron wire or sheet 28 may be between, e.g., approximately 200° C.and approximately 150° C. to anneal the iron and nitrogen mixture toform an iron nitride material having a Fe₁₆N₂ phase constitutionsubstantially throughout the thickness or diameter of iron wire or sheet28. Urea 72 and iron wire or sheet 28 may be at the annealingtemperature, e.g., between approximately 1 hour and approximately 40hours. Such an annealing process could be used in addition to or as analternative to other nitrogen diffusion techniques, e.g., when the ironmaterial is single crystal iron wire and sheet, or textured iron wireand sheet with thickness in micrometer level. In each of annealing andquenching, nitrogen may diffuse into iron wire or sheet 28 from thenitrogen gas or gas mixture including Ar plus hydrogen carrier gaswithin furnace 68. In some examples, gas mixture may have a compositionof approximately 86% Ar+4% H₂+10% N₂. In other examples, the gas mixturemay have a composition of 10% N₂+90% Ar or 100% N₂ or 100% Ar.

As will be described further below, the constitution of the iron nitridematerial formed via the urea diffusion process may be dependent on theweight ratio of urea to iron used. As such, in some examples, the weightratio of urea to iron may be selected to form an iron nitride materialhaving a Fe₁₆N₂ phase constitution. However, such a urea diffusionprocess may be used to form iron nitride materials other than thathaving a Fe₁₆N₂ phase constitution, such as, e.g., Fe₂N, Fe₃N, Fe₄N,Fe₈N, and the like. Moreover, the urea diffusion process may be used todiffuse nitrogen into materials other than iron. For example, such anurea diffusion process may be used to diffuse nitrogen into there areIndium, FeCo, FePt, CoPt, Cobalt, Zn, Mn, and the like.

Regardless of the technique used to nitridize iron wire or sheet 28(14), the nitrogen may be diffused into iron wire or sheet 28 to aconcentration of about 8 atomic percent (at. %) to about 14 at. %, suchas about 11 at. %. The concentration of nitrogen in iron may be anaverage concentration, and may vary throughout the volume of iron wireor sheet 28. In some examples, the resulting phase constitution of atleast a portion of the nitridized iron wire or sheet 28 (afternidtridizing iron wire or sheet 28 (14)) may be α′ phase Fe₈N. The Fe₈Nphase constitution is the chemically disordered counterpart ofchemically-ordered Fe₁₆N₂ phase. A Fe₈N phase constitution is also has abct crystal cell, and can introduce a relatively high magnetocrystallineanisotropy.

In some examples, the nitridized iron wire or sheet 28 may be α″ phaseFe₁₆N₂. FIG. 8 is an iron nitrogen phase diagram. As indicated in FIG.8, at an atomic percent of approximately 11 at. % N, α″ phase Fe₁₆N₈ maybe formed by quenching an Fe—N mixture at a temperature aboveapproximately 650° C. for a suitable amount of time. Additionally, at anatomic percent of approximately 11 at. % N, α″ phase Fe₁₆N₈ may beformed by annealing an Fe—N mixture at a temperature below approximately200° C. for a suitable amount of time

In some examples, once iron wire or sheet 28 has been nitridized (14),iron wire or sheet 28 may be annealed at a temperature for a time tofacilitate diffusion of the nitrogen atoms into appropriate interstitialspaces within the iron lattice to form Fe₁₆N₂ (16). FIG. 4 illustratesan example of the appropriate interstitial spaces of the iron crystallattice in which nitrogen atoms are positioned. In some examples, thenitridized iron wire or sheet 28 may be annealed at a temperaturebetween about 100° C. and about 300° C. In other examples, the annealingtemperature may be about 126.85° C. (about 400 Kelvin). The nitridizediron wire or sheet 28 may be annealed using Crucible heating stage 26, aplasma arc lamp, a radiation heat source, such as an infrared heat lamp,an oven, or a closed retort.

The annealing process may continue for a predetermined time that issufficient to allow diffusion of the nitrogen atoms to the appropriateinterstitial spaces. In some examples, the annealing process continuesfor between about 20 hours and about 100 hours, such as between about 40hours and about 60 hours. In some examples, the annealing process mayoccur under an inert atmosphere, such as Ar, to reduce or substantiallyprevent oxidation of the iron. In some implementations, while iron wireor sheet 28 is annealed (16) the temperature is held substantiallyconstant.

Once the annealing process has been completed, iron wire or sheet 28 mayinclude a Fe₁₆N₂ phase constitution. In some examples, at least aportion of iron wire or sheet 28 consists essentially of a Fe₁₆N₂ phaseconstitution. As used herein “consists essentially of” means that theiron wire or sheet 28 includes Fe₁₆N₂ and other materials that do notmaterially affect the basic and novel characteristics of the Fe₁₆N₂phase. In other examples, iron wire or sheet 28 may include a Fe₁₆N₂phase constitution and a Fe₈N phase constitution, e.g., in differentportions of iron wire or sheet 28. Fe₈N phase constitution and Fe₁₆N₂phase constitution in the wires and sheets and the later their pressedassemble may exchange-couple together magnetically through a workingprinciple of quantum mechanics. This may form a so-calledexchange-spring magnet, which may increase the magnetic energy producteven just with a small portion of Fe₁₆N.

In some examples, as described in further detail below, iron wire orsheet 28 may include dopant elements or defects that serve as magneticdomain wall pinning sites, which may increase coercivity of iron wire orsheet 28. As used herein, an iron wire or sheet 28 that consistsessentially of Fe₁₆N₂ phase constitution may include dopants or defectsthat serve as domain wall pinning sites. In other examples, as describedin further detail below, iron wire or sheet 28 may include non magneticdopant elements that serve as grain boundaries, which may increasecoercivity of iron wire or sheet. As used herein, an iron wire or sheet28 that consists of Fe₁₆N₂ phase constitution may include non magneticelements that serve as grain boundaries.

Once the annealing process has been completed, iron wire or sheet 28 maybe cooled under an inert atmosphere, such as argon, to reduce or preventoxidation.

In some examples, iron wire or sheet 28 may not be a sufficient size forthe desired application. In such examples, multiple iron wire or sheets28 may be formed (each including or consisting essentially of a Fe₁₆N₂phase constitution) and the multiple iron wire or sheets 28 may bepressed together to form a larger permanent magnet that includes orconsists essentially of a Fe₁₆N₂ phase constitution (18).

FIGS. 5A and 5B are conceptual diagrams that illustrate an example ofthe compression process. As shown in FIG. 5A, multiple iron wire orsheets 28 are arranged such that the <001> axes of the respective ironwire or sheets 28 are substantially aligned. In examples in which the<001> axes of the respective iron wire or sheets 28 are substantiallyparallel to a long axis of the wire or sheet 28, substantially aligningthe iron wire or sheets 28 may include overlying one iron wire or sheet28 on another iron wire or sheet 28. Aligning the <001> axes of therespective iron wires or sheets 28 may provide uniaxial magneticanisotropy to permanent magnet 52.

The multiple iron wires or sheets 28 may be compressed using, forexample, cold compression or hot compression. In some examples, thetemperature at which the compression is performed may be below about300° C., as Fe₁₆N₂ may begin to degrade above about 300° C. Thecompression may be performed at a pressure and for a time sufficient tojoin the multiple iron wires or sheets 28 into a substantially unitarypermanent magnet 52, as shown in FIG. 5B.

Any number of iron wires or sheets 28 may be pressed together to formpermanent magnet 52. In some examples, permanent magnet 52 has a size inat least one dimension of at least 0.1 mm. In some examples, permanentmagnet 52 has a size in at least one dimension of at least 1 mm. In someexamples, permanent magnet 52 has a size in at least one dimension of atleast 1 cm.

In some examples, in order to provide desirable high coercivity, it maybe desirable to control magnetic domain movement within iron wire orsheet 28 and/or permanent magnet 52. One way in which magnetic domainmovement may be controlled is through introduction of magnetic domainwall pinning sites into iron wire or sheet 28 and/or permanent magnet52. In some examples, magnetic domain wall pinning sites may be formedby introducing defects into the iron crystal lattice. The defects may beintroduced by injecting a dopant element into the iron crystal latticeor through mechanical stress of the iron crystal lattice. In someexamples, the defects may be introduced into the iron crystal latticebefore introduction of nitrogen and formation of the Fe₁₆N₂ phaseconstitution. In other examples, the defects may be introduced afterannealing iron wire or sheet 28 to form Fe₁₆N₂ (16). One example bywhich defects that serve as domain wall pinning sites may be introducedinto iron wire or sheet 28 may be ion bombardment of boron (B), copper(Cu), carbon (C), silicon (Si), or the like, into the iron crystallattice. In other examples, powders consisting of non magnetic elementsor compounds (e.g. Cu, Ti, Zr, Ta, SiO₂, Al₂O₃, etc) may be pressedtogether with the iron wires and sheets that comprising of Fe₁₆N₂ phase.Those non magnetic powders, with the size ranging from severalnanometers to several hundred nanometers, function as the grainboundaries for Fe₁₆N₂ phase after pressing process. Those grainboundaries may enhance the coercivity of the permanent magnet.

Although described with regard to iron nitride, one or more of theexamples processes describe herein may also apply to FeCo alloy to formsingle crystal or highly textured FeCo wires and sheets. Co atoms mayreplace part of Fe atoms in Fe lattice to enhance the magnetocrystallineanisotropy. Additionally, one or more of the examples strained diffusionprocesses described herein may also apply to these FeCo wires andsheets. Furthermore, one or more of the examples processes may alsoapply to diffuse Carbon (C), Boron (B) and Phosphorus (P) atoms into Feor FeCo wires and sheets, or partially diffuse C, P, B into Fe or FeCowires and sheets together with N atoms. Accordingly, the methodsdescribed herein may also apply to FeCo alloy to form single crystal orhighly textured FeCo wires and sheets. Also, Co atoms may replace partof Fe atoms in Fe lattice, e.g., to enhance the magnetocrystallineanisotropy. Further, the method described herein may also apply todiffuse Carbon (C), Boron (B) and Phosphorus (P) atoms into Fe or FeCowires and sheets, or partially diffuse C, P, B into Fe or FeCo wires andsheets together with N atoms. Moreover, the iron used for the processesdescribed herein may take the shape of wire, sheet, or bulk form.

Example

A series of experiments were carried out to evaluate one or more aspectsof example iron nitride materials described herein. In particular,various examples iron nitride materials were formed via urea diffusionand then evaluated. The weight ratio of urea to bulk iron was varied todetermine the dependence of the constitution of iron nitride material onthis ratio. As shown in FIG. 12, five different examples were formedusing urea to iron weight ratios of approximately 0.5 (i.e., 1:2), 1.0,1.2, 1.6, and 2.0.

For reference, at temperatures above approximately 1573° C., the mainchemical reaction process for the described urea diffusion process is:CO(NH₂)₂→NH₃+HNCO  (1)HNCO+H₂O→2NH₃+CO₂  (2)2NH₃→2N+3H₂  (3)2N→N₂  (4)In such a reaction process, for the nitrogen atom, it may be relativelyeasy to recombine into a molecule, as shown in equation (4).Accordingly, in some examples, the recombination of nitrogen atoms maybe decreased by placing the urea next to or proximate to the bulk ironmaterial during a urea diffusion process. For example, in some cases,the urea may be in direct contact with the surface of the bulk ironmaterial, or within approximately 1 centimeter of the bulk material

The iron nitride samples were prepared according to the urea diffusionprocess described herein. Following the preparation of the iron nitridesample via the urea diffusion process, Auger electron spectroscopy wasused to determine the chemical composition on the surface of the exampleiron materials. FIG. 9 is a plot of the Auger measurement results forone of the examples, which indicates the presence of nitrogen in thematerial.

FIG. 12 is plot of weight ratio of urea to bulk iron material used inthe urea diffusion process versus nitrogen concentration (at. %) of thefinal iron nitride material. As noted above, ratios of 0.5 (i.e., 1:2),1.0, 1.2, 1.6, and 2.0 for urea to bulk iron material where used. Asshown in FIG. 12, different weight ratios of urea to iron may lead todifferent nitrogen concentrations within the iron nitride materialfollowing urea diffusion. In particular, FIG. 12 illustrates that theatomic ratio of nitrogen in the iron nitride material increased as theamount of urea used relative to the amount bulk iron increased.Accordingly, in at least some cases, the desired nitrogen concentrationof an iron nitride material formed via urea diffusion may be obtained byusing the weight ratio of urea to iron in the starting materialcorresponding to the desired nitrogen concentration.

FIG. 10 is plot of depth below the surface of the iron nitride materialversus concentration (at. %) for the iron nitride material formed viaurea diffusion starting with a weight ratio of urea to iron ofapproximately 2.0. As shown in FIG. 10, the concentration of nitrogenfrom the surface of the iron nitride material to approximately 1600angstroms below the surface of the material was approximately 6 at. %.Moreover, there isn't any trace for oxygen and carbon, which means thatother dopant source(s) have been diminished effectively.

FIG. 11 is a plot of depth below the surface of the iron nitridematerial versus concentration (at. %) for the iron nitride materialformed via urea diffusion starting with a weight ratio of urea to ironof approximately 1.0. As shown in FIG. 11, the concentration of nitrogenfrom the surface of the iron nitride material to approximately 800angstroms below the surface of the material was approximately 6-12 at.%. In some examples, the concentration could be reduced further byimproving the vacuum system, e.g., such as using pumping system to causegreater flow. As also show, oxygen has been diminished to be about 4 at.%. Although there is over 10 at. % carbon, since it can be considered asubstitute element for nitrogen, it has no significant negative effecton the fabricated permanent magnet.

One example method comprises straining an iron wire or sheet comprisingat least one iron crystal in a direction substantially parallel to a<001> crystal axis of the iron crystal to distort a unit cell structureof the at least one iron crystal and form a distorted unit cellstructure having an increased length along the <001> crystal axis. Themethod further comprises nitridizing the iron wire or sheet to form anitridized iron wire or sheet, and annealing the nitridized iron wire orsheet to form a Fe16N2 phase constitution at least a portion of thenitridized iron wire or sheet.

In the example method, straining the iron wire or sheet comprising theat least one iron crystal in the direction substantially parallel to the<001> crystal axis of the iron crystal may comprise applying a tensileforce to the iron wire or sheet by pulling a first end of the iron wireor sheet in a first direction and pulling the second end of the ironwire or sheet in a second direction substantially opposite to the firstdirection.

In the example method, heating the iron wire or sheet to a temperaturebetween about 125° C. and about 600° C. may comprise heating the ironwire or sheet to a temperature of about 125° C. for about 8.85 hours.

In the example method, heating the iron wire or sheet to a temperatureof between about 125° C. and about 600° C. may comprise heating the ironwire or sheet to a temperature of about 600° C. for about 2.4 hours.

In the example method, nitridizing the iron wire or sheet to form thenitridized iron wire or sheet may comprise exposing the iron wire orsheet to an atomic nitrogen substance.

In the example method, the nitrogen precursor may be mixed with acarrier gas. The nitrogen precursor may be mixed with the carrier gas toa partial pressure of between about 0.02 and about 0.1.

In the example method, exposing the iron wire or sheet to the atomicnitrogen substance may comprise exposing the iron wire or sheet to anitrogen precursor at a pressure between about 0.133 Pa and about 1333Pa.

In the example method, annealing the nitridized iron wire or sheet toform the Fe₁₆N₂ phase constitution in at least the portion of thenitridized iron wire or sheet may comprise heating the nitridized ironwire or sheet to between about 100° C. and about 300° C. for betweenabout 20 hours and about 100 hours.

In the example method, annealing the nitridized iron wire or sheet toform the Fe₁₆N₂ phase constitution in at least the portion of thenitridized iron wire or sheet may comprise annealing the nitridized ironwire or sheet under an inert atmosphere.

The example method may further comprise compressing a plurality ofnitridized iron wires or sheets comprising a Fe₁₆N₂ phase constitutionto form a permanent magnet comprising a Fe₁₆N₂ phase constitution.

In the example method, compressing the plurality of nitridized ironwires or sheets may comprise the Fe₁₆N₂ phase constitution to form thepermanent magnet comprising the Fe₁₆N₂ phase constitution comprises coldcompressing the plurality of nitridized iron wires or sheets comprisingthe Fe₁₆N₂ phase constitution to form the permanent magnet comprisingthe Fe₁₆N₂ phase constitution.

In the example method, compressing the plurality of nitridized ironwires or sheets comprising the Fe₁₆N₂ phase constitution to form thepermanent magnet comprising the Fe₁₆N₂ phase constitution may comprisesubstantially aligning a <001> crystal axis of a first nitridized ironwire or sheet comprising the Fe₁₆N₂ phase constitution with a <001>crystal axis of a second nitridized iron wire or sheet comprising theFe₁₆N₂ phase constitution prior to compressing the first nitridized ironwire or sheet and the second iron wire or sheet.

In the example method, compressing the plurality of nitridized ironwires or sheets comprising the Fe₁₆N₂ phase constitution to form thepermanent magnet comprising the Fe₁₆N₂ phase constitution may comprisecompressing the plurality of nitridized iron wires or sheets comprisingthe Fe₁₆N₂ phase constitution to form the permanent magnet comprisingthe Fe₁₆N₂ phase constitution and defining a size in at least onedimension of at least 0.1 mm.

In the example method, compressing the plurality of nitridized ironwires or sheets comprising the Fe₁₆N₂ phase constitution to form thepermanent magnet comprising the Fe₁₆N₂ phase constitution may comprisecompressing the plurality of nitridized iron wires or sheets comprisingthe Fe₁₆N₂ phase constitution to form the permanent magnet comprisingthe Fe₁₆N₂ phase constitution and defining a size in at least onedimension of at least 1 mm.

In the example method, nitridizing the iron wire or sheet to form thenitridized iron wire or sheet may comprise exposing the iron wire orsheet to an atomic nitrogen substance, wherein the atomic nitrogensubstance is formed from urea.

In the example method, introducing magnetic domain wall pinning sitesinto the nitridized iron wire or sheet may comprise ion bombarding thenitridized iron wire or sheet with a dopant element.

In one example, a system comprises a strain inducing apparatusconfigured to exert a strain on an iron wire or sheet comprising atleast one body centered cubic (bcc) iron crystal in a directionsubstantially parallel to a <001> axis of the bcc iron crystal, a firstheating apparatus configured to heat the strained iron wire or sheet, asource of an atomic nitrogen substance configured to expose the strainediron wire or sheet to the atomic nitrogen substance to form a nitridizediron wire or sheet, and a second heating apparatus configured to heatthe nitridized iron wire or sheet to a temperature sufficient to annealthe nitridized iron wire or sheet to form a Fe₁₆N₂ phase constitution inat least a portion of the nitridized iron wire or sheet.

The example system may further comprises a press configured to compressa plurality of nitridized iron wire or sheets comprising a Fe₁₆N₂ phaseconstitution to form a substantially unitary permanent magnet includinga Fe₁₆N₂ phase constitution.

The press may be configured to compress a plurality of nitridized ironwires or sheets comprising the Fe₁₆N₂ phase constitution to form asubstantially unitary permanent magnet including the Fe₁₆N₂ phaseconstitution and defining a size in at least one dimension of at least0.1 mm.

The press may be configured to compress a plurality of nitridized ironwires or sheets comprising the Fe₁₆N₂ phase constitution to form asubstantially unitary permanent magnet including the Fe₁₆N₂ phaseconstitution and defining a size in at least one dimension of at least 1mm.

The source of the atomic nitrogen substance may comprise urea.

The example system may further comprise means for introducing magneticdomain wall pinning sites into the nitridized iron wire or sheet.

The strain inducing apparatus may comprise a first roller configured toreceive a first end of the iron wire or sheet and a second rollerconfigured to receive a second end of the iron wire or sheet, whereinthe second end is substantially opposite the first end, and wherein thefirst roller and the second roller are configured to rotate to apply atensile force between the first end of the iron wire or sheet and thesecond end of the iron wire or sheet.

The first roller and the second roller are configured to rotate tostrain the iron wire or sheet between about 0.3% and about 7.0%.

The first heating apparatus may comprise, for example, a crucibleheating stage, a radiation heat source or a plasma arc lamp.

The second heating apparatus may comprise, for example, a heatingcrucible, radiation heat source, a plasma arc lamp, an oven or a closedretort.

In one example, a permanent magnet comprises a wire comprising a Fe₁₆N₂phase constitution. In the example permanent magnet, the wire may have adiameter of at least about 0.01 millimeters. In other examples, the wiremay have a diameter of about 0.1 millimeters.

In the example permanent magnet, the wire may have an energy product ofgreater than about 30 MGOe. In other examples, the wire has an energyproduct of greater than about 60 MGOe. In other examples, the wire hasan energy product of greater than about 65 MGOe. In other examples, thewire has an energy product of greater than about 100 MGOe. In otherexamples, the wire has an energy product of between about 60 MGOe andabout 135 MGOe.

In the example permanent magnet, the wire defines a major axis extendingfrom a first end of the wire to a second end of the wire, wherein thewire comprises at least one body centered tetragonal (bct) iron nitridecrystal, and wherein a <001> axis of the at least one bct iron nitridecrystal is substantially parallel to the major axis of the wire.

In one example, the permanent magnet may comprise at least one magneticdomain wall pinning site.

The example permanent magnet may further comprise a phase stabilizationdopant element comprising at least one of Ti, Co, Ti, Ta, Ni, Mn, Zr,Mo, Nb, Nd, Ga, Ge, C, B, Si, P, Cr, Cu, or Zn.

In one example, the wire of the permanent magnet comprises a Fe₈N phaseconstitution. In another example, the wire of the permanent magnetconsists essentially of the Fe₁₆N₂ phase constitution.

In another example, a permanent magnet comprises a sheet comprising aFe₁₆N₂ phase constitution.

In some examples, the sheet may have a thickness of at least about 0.01millimeters. In other examples, the sheet has a thickness of about 0.1millimeters.

The sheet may have an energy product of greater than about 30 MGOe. Inother examples, the sheet may have an energy product of greater thanabout 60 MGOe. In other examples, the sheet has an energy product ofgreater than about 65 MGOe. In other examples, the sheet has an energyproduct of greater than about 100 MGOe. In other examples, the sheet hasan energy product of between about 60 MGOe and about 135 MGOe.

In examples of the permanent magnet, the sheet defines a major axisextending from a first end of the sheet to a second end of the sheet,wherein the sheet comprises at least one body centered tetragonal (bct)iron nitride crystal, and wherein a <001> axis of the at least one bctiron nitride crystal is substantially parallel to the major axis of thesheet.

In examples of the permanent magnet, the sheet further comprises a Fe₈Nphase constitution.

In examples of the permanent magnet, the sheet consists essentially ofthe Fe₁₆N₂ phase constitution.

In another example, a permanent magnet comprises a Fe₁₆N₂ phaseconstitution, wherein the permanent magnet has a size in at least onedimension of at least 0.1 mm. In some examples, the permanent magnet hasa size in at least one dimension of at least 1 mm. In some examples, thepermanent magnet has a size in at least one dimension of at least 1 cm.

The permanent magnet may have an energy product of greater than about 30MGOe. In other examples, the permanent magnet may have an energy productof greater than about 60 MGOe. In other examples, the permanent magnetmay have an energy product of greater than about 65 MGOe. In otherexamples, the permanent magnet may have an energy product of greaterthan about 100 MGOe. In other examples, the permanent magnet may have anenergy product of between about 60 MG*Oe and about 135 MG*Oe.

The permanent magnet may comprise a Fe₈N phase constitution. In anotherexample, the permanent magnet consists essentially of the Fe₁₆N₂ phaseconstitution.

Another example method comprises nitridizing a metallic member via aurea diffusion process.

In one example, nitridizing a metallic member via the urea diffusioncomprises heating urea and the metallic member together within a chamberto a temperature selected to decompose nitrogen atoms of the urea,wherein the nitrogen atoms diffuse into the metallic member within thechamber

The metallic member may comprise iron. In another example, the metallicmember consists essentially of iron. In one example, a ratio of urea toiron is selective such that, after the urea diffusion process, themetallic member consists essentially of the Fe₁₆N₂ phase constitution.

Various examples have been described. These and other examples fallwithin the scope of the following claims.

What is claimed is:
 1. A method comprising: straining an iron wire or sheet comprising at least one iron crystal in a direction parallel to a <001> crystal axis of the at least one iron crystal to distort a unit cell structure of the at least one iron crystal and form a distorted unit cell structure having an increased length along the <001> crystal axis; while straining the iron wire or sheet, nitridizing the iron wire or sheet to form a nitridized iron wire or sheet; and annealing the nitridized iron wire or sheet to form a Fe16N2 phase constitution in at least a portion of the nitridized iron wire or sheet.
 2. The method of claim 1, wherein the iron wire or sheet comprises a single iron crystal structure or textured structure.
 3. The method of claim 1, wherein the iron wire or sheet comprises a plurality of iron crystals, and wherein straining the iron wire or sheet comprising the at least one iron crystal in the direction parallel to the <001> crystal axis of the iron crystal comprises straining the iron wire or sheet comprising the plurality of iron crystals in a direction parallel to the <001> crystal axis of at least some of the plurality of iron crystals.
 4. The method of claim 1, wherein the iron wire or sheet comprises the iron wire, wherein the iron wire defines a major axis, and wherein straining the iron wire or sheet comprising the at least one iron crystal in the direction parallel to the <001> crystal axis of the iron crystal comprises straining the iron wire in the direction parallel to the major axis of the iron wire.
 5. The method of claim 1, wherein straining the iron wire or sheet comprising the at least one iron crystal in the direction parallel to the <001> crystal axis of the iron crystal comprises straining the iron wire or sheet comprising the at least one iron crystal in the direction parallel to the <001> crystal axis of the iron crystal to a strain of between about 0.3% and about 7%.
 6. The method of claim 1, wherein nitridizing the iron wire or sheet to form the nitridized iron wire or sheet comprises: exposing the iron wire or sheet to an atomic nitrogen substance; and heating the iron wire or sheet to a temperature between about 125° C. and about 600° C.
 7. The method of claim 6, wherein the atomic nitrogen substance is formed from a nitrogen precursor comprising at least one of N2 gas, NH3 gas, or urea.
 8. The method of claim 1, wherein annealing the nitridized iron wire or sheet to form the Fe16N2 phase constitution in at least the portion of the nitridized iron wire or sheet comprises heating the nitridized iron wire or sheet to between about 100° C. and about 300° C. under an inert atmosphere.
 9. The method of claim 1, further comprising introducing magnetic domain wall pinning sites into the nitridized iron wire or sheet comprising the Fe16N2 phase constitution.
 10. The method of claim 9, wherein introducing magnetic domain wall pinning sites into the nitridized iron wire or sheet comprising the Fe16N2 phase constitution comprises ion bombarding the nitridized iron wire or sheet comprising the Fe16N2 phase constitution with a dopant element.
 11. The method of claim 1, further comprising introducing magnetic domain wall pinning sites into the nitridized iron wire or sheet prior to straining the iron wire or sheet comprising the at least one iron crystal in the direction parallel to the <001> crystal axis of the iron crystal.
 12. The method of claim 1, further comprising introducing a phase stabilization dopant element comprising at least one of Ti, Co, Ti, Ta, Ni, Mn, Zr, Mo, Nb, Nd, Ga, Ge, C, B, Si, P, Cr, Cu, or Zn into the iron wire or sheet.
 13. The method of claim 1, wherein the distorted unit cell structure defines a body centered tetragonal (bct) iron crystal unit cell elongated along a <001> axis between about 0.3% and about 7% compared to an unstrained iron body centered cubic (bcc) crystal unit cell. 